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15. 15. Bored hole size before tapping ( for thread cutting )

  • Recommended Bored Hole Size Table for Taper Pipe Threads (PT) (refer to JIS B 0203) <Remarks during tapping> ・PT internal threads have R design on their crests. The taps should cut threads with their thread root. ・ On thread having non-full threads, if you are going to cut effective thread length ℓ, use the tap of long type.

unit: mm

ThreadStandardsMinor DiameterRecommended Boredreference
SizeBasic DiameterBasic Diameter PositionEffective T (Minf hread Length imum)Pipe End (Workpiece Face)When Threads have non-Full ThreadsWhen Threads do not have the non-Full ThreadsHole Sizes Maximum S Bore(reference) ize of Straight d HoleT Basic D Pos ℓap iameter ition, g
Tolerance in radial directionPipe End Tolerance in axial direction cWhen Threads have non-Full Threads 1) ℓWhen Threads do not have the non-Full Threads 1) t(Basic Diamater ) Basic SizePosition away from Pipe End by ℓ Basic SizePosition away from Pipe End by t Basic SizeWhen Threads have non-Full ThreadsWhen Threads do not have the non-Full ThreadsLong Thread TypeShort Thread Type
①②③④⑤⑥⑦⑧⑨⑩⑪⑫
PT1/16- 28±0.071±1.136.24.46.5616.1746.2866.16.213.010.5
PT1/8 - 28±0.071±1.136.24.48.5668.1798.2918.18.213.010.5
PT1/4 - 19±0.104±1.679.46.711.44510.85811.02610.710.921.012.5
PT3/8 - 19±0.104±1.679.77.014.95014.34414.51314.214.421.014.0
PT1/2 - 14±0.142±2.2712.79.118.63117.83718.06217.617.925.017.0
PT3/4 - 14±0.142±2.2714.110.224.11723.23623.48023.023.325.019.0
PT1 - 11±0.181±2.8916.211.630.29129.27929.56629.029.332.022.0
PT11/4 - 11±0.181±2.8918.513.438.95237.79638.11537.637.932.024.5
PT11/2 - 11±0.181±2.8918.513.444.84543.68944.00843.543.832.025.5
PT2 - 11±0.181±2.8922.816.956.65655.23155.60055.055.435.028.0

Note 1) Length toward End of Smaller Diameter from Baisc Diameter Position

When Threads have When Threads do not have non-Full Threads the non-Full Threads ⑥ ⑥ Basic Diameter Position

⑦ ⑧

Remarks 1. Opening of Internal Thread (Face of workpiece) is Basic

Diameter Position.

Remarks 2. Effective Thread Length has 2 types, with non-Full Thread

Type and without non-Full Thread Type. Remarks 3. Concerning bored hole shape, considering load on taps, taper bored hole is recommended.

Remarks 4. When applying taper bored hole, by referring to values

shown in columns ②·⑥~⑧, prepare the taper hole by

using pipe reamer (1/16 taper). By referring to values

shown in columns ⑨ and ⑩, select the drill diameter

before reaming by taking reamer's margin into account.

Remarks 5. When preparing straight bored hole, by referring to

values shown in columns ⑨ and ⑩, select drill diameter.